This invention relates to a programmed welding machine with a continuously monitored override control.
Welding machines which have a programming device associated therewith for directing the welding head along a predetermined path have long been in use. The programming device may include such apparati as numerical control (N/C), templates with tracer followers and the like. The welding machines have been used to manufacture large parts such as booms, c-frames, vehicle lift arms, etc., which may include not only straight line segments but also contoured segments.
In the manufacture of large parts such as those mentioned above, they have often been formed from an assembly of two or more individual pieces which have been initially created by flame cutting them with plasma or like torches from a large workpiece. The individual pieces are then tack welded if desired and fixedly positioned adjacent each other to form a groove or seam. A welding head is then moved along the groove to apply a bead which joins the pieces together.
In addition, contouring devices are already known which include a transverse beam or bridge which defines a transverse or X axis and which is movable along rails or the like which define a longitudinal or Y axis. A carriage mounted for movement along the bridge carries a metal working tool, such as a cutting torch or the like.
Furthermore, it is known to mount a sensing means such as a probe adjacent a welding head for the purpose of sensing the position of the edge of a groove or seam for welding, and to broadly provide a slide mechanism for adjusting the position of the welding head in accordance with the positional output of the probe.
It has long been desired to provide a welding machine that is truly universal, that is, one which will accurately weld almost any desired contour without the need for major readjustments in the mechanism. Unfortunately, to the knowledge of the inventor, this has not previously been possible, even with pre-programmed controls.
One of the major problems has been that, even though almost any contour can be programmed via N/C or tracer devices, the groove to which the welding material is to be applied does not usually conform to the desired contour exactly. This non-conformity is unpredictable and may be the result of a number of actors, one of the most significant being that the edges of the pieces to be joined often cannot be originally flame cut or otherwise formed to a very close tolerance. The tolerance in flame cutting may be as much as 1/4 inch or more. This large tolerance may make it difficult, if not impossible, to create a final welded seam that is structurally sound throughout its length, even with a programmed weld head contouring control. Another problem occurs because tack welding of pieces to be welded introduces heat to the parts, thereby causing distortion.
As a result of the above problems, the practice in the past has been to design a different welding machine for weldments of differing shapes and to solve the tolerance problem in the design of each particular machine.
It is a task of the present invention to provide a programmed welding machine that will accurately join large pieces along any desired contour without the need for major readjustments of the machine when welding parts of different shape.
It is a further task of the invention to provide a programmed welding machine that will automatically compensate for deviations in the contours in the weldments when welding many parts of the same general shape, or when welding parts of different shape.
It is another task of the invention to provide a programmed welding machine wherein the weld head is driven along a programmed path which corresponds to the desired general weld contour, and wherein deviations from that contour in the welding groove between the parts are compensated for to cause the weld head to be driven along the exact path dictacted by the parts themselves. The said exact path is, at least at times, different from the programmed path.
It is yet a further task of the present invention to continuously compensate for the said contour deviations in a manner that does not affect or change the basic programming control, and to place the weld where in reality it should be rather than where it was programmed to be.
The invention is contemplated for use in connection with a welding machine wherein main horizontal X and Y axes are defined. A mounting device is carried beneath the carriage of the welding machine, for mounting an assembly comprising a welding head and a weld groove sensor. This mounting device comprises a rotor which defines a vertical C axis about which the tips of the welding head and sensor can be rotated.
A programming device, such as a numerical control arrangement or a tracer, is programmed in the usual manner to move the machine parts, and thus the welding head and sensor assembly, relative to the main X and Y axes, and may be used to turn the rotator so that the said assembly turns about the C axis. Programmed turning of the assembly is for the purpose of maintaining the sensor in a position ahead of the welding head along the welding groove, no matter what the contour thereof. A feedback from the main drive motors for the machine and rotator satisfies the programming device that the welding head and sensor assembly is where it is programmed to be.
Broadly, the inventive concept is deriected to overriding the programming device in a manner so that the welding head is continuously moved from the programmed path to a desired corrected path defined by deviations in the weld groove, without affecting the program.
A slide assembly is connected between the machine carriage and the welding head and sensor assembly, with the slide assembly defining a plurality of axes of deviation, such as X.sub.d and Y.sub.d. The slide assembly is adapted to be driven by motors, one for each axis of deviation, to cause translation of the welding head from its programmed path to the desired deviated path in accordance with the deviaton in the weld groove.
For purposes of control of the slide motors, the shaft of a sine-cosine resolver is gearingly connected in a one-to-one relationship to a gear forming part of the rotator. The stator windings of the resolver are connected to the slide motors and are responsive to a voltage fed to the resolver rotor or shaft winding. The stator winding signal is responsive to the deviated position of the sensor in the weld groove relative to the programmed weld head position and, depending upon the amount of deviation, drives the slide motors to provide a correction in the welding head position.
The rotary position of the resolver shaft, and thus the rotor winding, relative to the stator windings, provides a settling of the resolver which determines the ratio of the relative corrective drive signals to be fed to the slide motors. The resolver shaft's rotary position is, in turn, responsive to the rotary position of the rotator, through the gearing connection.
As the welding machine is operated, the programming device drives the welding head along a straight or contoured path relative to the main X and Y axes, which is the generally desired path for forming the weld in a groove between two pieces to be joined. At the same time, the programming device may turn the rotator when necessary about the vertical C axis to maintain the sensor ahead of the welding head. Deviations from the programmed path in a direction perpendicular thereto are sensed by the sensor which, through the resolver, instructs the slide motors to move the welding head from its programmed path and along the X.sub.d and/or Y.sub.d axes to the actual desired deviated path.
Although the welding head is caused to deviate from its programmed path when needed, the programming device is unaffected thereby and may be used to weld other identical pieces which may have different deviations.